Horizontal directional drilling is a type of underground horizontal directional drilling. Horizontal directional drills that are capable of drilling through rock are configured to drill through dirt and many different rocky terrains while simultaneously being steered. Horizontal rock drilling may use a tri cone bit configuration. The bit is steered by adding asymmetry to the bit relative to the adjacent bore walls. The asymmetry is typically achieved by is incorporating some form of a deflection device or steering member some distance behind the bit, such as a deflection shoe or a bend in the casing that inherently comprises a deflection shoe. The orientation of the deflection device or steering member is preferably kept stable about the bore axis during the steering operation.
Progressive cavity motors, also known as mud motors, incorporate the bend feature and have been used to steer the drill bit. The motors couple the outer casing of the drill string and integrate the bend into the outer casing. The motors are actuated by a very high flow of drilling fluid or mud through the motor. Mud flow rotates the motor shaft and works to turn the bit without rotation of the drill string. By maintaining a stationary position of the bend about the bore axis while continuing to drill, deviation is accumulated and the process of directional drilling is achieved. High mud flow rates are required to use these motors which can sometimes be undesirable.
Rotary steering tools may also be used to steer the bit. The rotary steering tool incorporates the bend concept and couples the tricone bit directly to the drill stem, such that the bit is actuated by rotation of the drill stem. The bend is then preferably coupled to something to prevent its rotation about the bore axis. The bore wall is typically used as the stabilizer. However, if the friction between the bore wall and the bend is too much or too little, the use of the steering tool may be inefficient.
A third method utilizes a dual drill pipe system that has the steering bend coupled to the outer pipe and the tricone bit is rotated via the inner pipe which is concentric to the outer pipe. The outer pipe of the dual drill pipe system is not rotated during a steering deviation.
The present invention provides the ability to keep the drill stem rotating during the steering process and keep a bend position about the bore axis without utilizing the compressive and shear strength of the bore wall. The present invention also uses less fluid to operate the motor than typical progressive cavity motors.